[issues] Change the type of violatingNodeId in the DevTools Protocol

Addressing post-commit comments to CL: https://chromium-review.googlesource.com/c/chromium/src/+/2289841

Bug: chromium:1082628
Change-Id: I22ae9d66d9940f95a8faea654418e8aa9859e2b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2338796Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Kateryna Prokopenko <kprokopenko@google.com>
Cr-Commit-Position: refs/heads/master@{#795436}

third_party/blink/public/devtools_protocol/browser_protocol.pdl

@@ -623,7 +623,7 @@ experimental domain Audits
       ContentSecurityPolicyViolationType contentSecurityPolicyViolationType
       optional AffectedFrame frameAncestor
       optional SourceCodeLocation sourceCodeLocation
-      optional integer violatingNodeId
+      optional DOM.BackendNodeId violatingNodeId
 
   # A unique identifier for the type of issue. Each type may use one of the
   # optional fields in InspectorIssueDetails to convey more specific